The present invention relates to data processing systems, and more specifically, to automated modular cabinets for storing and accessing data storage media such as tape cartridges, magnetic disks, and optical disks.
Magnetic tape cartridges, magnetic disks, and optical disks are all widely used as peripheral memory storage devices for computer systems. Large computer systems often operate in conjunction with external libraries of dozens of media elements as well as the media element readers used to retrieve and record data. Although originally such media elements were selected and loaded manually, automated libraries were developed to expedite the handling of the media. These systems include means for accessing a desired media element, retrieving it from its storage position, and loading it into an appropriate reader.
As data storage requirements for computer systems have increased from megabytes to gigabytes to terabytes, the development of automated media libraries has received considerable attention. Some embodiments of such libraries comprise a small number of magnetic tape cartridges, six or ten being typical, and one or two tape drives housed in a single enclosure. An automated library of this type is described in U.S. Pat. No. 4,918,548 to O'Donnell. This format has additionally been expanded on in two ways. In some systems, cabinet sized housings have been developed which hold a much larger number of tapes and drives, and which further comprise robotic arms, usually translatable on all three axes, which remove tapes from storage and place them in tape drives. An example of a system of this type is disclosed in U.S. Pat. No. 4,984,106 to Herger et al. In other systems, several smaller libraries are placed together in a single rack, and are provided with a common control system. A commercially available embodiment of such a system is the TapeFrame.TM. library from Spectra Logic in Boulder, Colo.
Modular systems have also been developed wherein media elements are housed in some modules of the system, and media element readers are housed in other modules. Two systems of this type are disclosed in U.S. Pat. No. 4,504,936 to Faber et al., and U.S. Pat. No. 5,285,333 to Barr et al. Such modular systems typically comprise a mechanism for moving media within each module, as well as a mechanism for moving media from module to module. An advantage of such systems is that increased data storage capacity and increased reading/writing capacity can be independently provided by adding either media or drive modules respectively.
Given the ever increasing data storage capacity requirements of modern computer systems, improvements in simplicity, cost, and system flexibility of tape and other storage media libraries is highly desirable. Specifically, it is desirable to provide media transfer robotics which utilize as few moving parts as possible. It is also desirable to provide system flexibility which allows the use of drive, media, and combination drive/media modules, and which allows easy interchangeability of the modules to adapt to changing host system requirements. The prior art has significant drawbacks in both of these areas.
In U.S. Pat. No. 5,285,333 to Barr et al. for example, a clamp type cartridge gripper is described which is attached to an elevator for transporting media vertically to different modules. Clamping grippers of this sort are widely used in media libraries to grasp and pull media cartridges from their storage locations. These grippers are complicated mechanically, and often fail to solidly grip the media. Furthermore, they are typically solenoid actuated, and therefore require an electrical connection to the library controller circuitry such that when provided on an elevator or other moving robotic arm, stress and wear of the interconnecting wiring is a concern. A clamping gripper is avoided in the system disclosed in U.S. Pat. No. 4,918,548 to O'Donnell et al. This patent discloses a pawl which engages a notch on a magnetic tape cartridge. Although some drawbacks of a clamping gripper are thereby avoided, a complicated articulating structure is utilized to ensure that the pawl engages the notch only at the appropriate time.
The modularity of the prior art has also been limited in scope. For example, the system disclosed in the Barr et al. patent mentioned above contains media modules and drives, but no combination media/drive modules. The same is true in the optical disc library infiniDISC.TM., commercially available from Dynatek in Toronto, Canada. Furthermore, library systems utilizing combination media/drive modules (such as the TapeFrame.TM. library mentioned above) have not provided for inter-module swapping of media.
Accordingly, it would be beneficial to provide data storage media libraries with increased simplicity, reduced cost, and increased flexibility over those currently available. Such an improved system should incorporate robotics having a minimum of moving parts, and should maximize the benefits of the modular format.